docs(claude): codify audit-before-assume principle as diagnostic discipline

New section in CLAUDE.md after "Order of work for each new module".

Three consecutive incidents in the timetable sprint led to formalising
this principle:

  - B1 (controller assumed buggy, seeder was wrong) — Phase A's
    schema-verify gate against SCHEMA.md:1285 + RFC §10.2 inverted the
    fix direction.
  - B5 (enum-shape assumed drifted, decimals were wrong) — Phase A's
    field-by-field response audit caught the actual decimal-as-string
    drift before any "fix" against the wrong hypothesis was written.
  - Timetable UX (test-passing layer diverged from prototype) — the
    mechanical-vs-UX split surfaced via browser test, not via the
    389-test suite which all agreed with the buggy state.

Pattern across all three: the initial hypothesis was wrong. The fix
prompts ALL gated Phase A as STOP-and-report; the schema/contract/
prototype audit was reviewed before any code was written. Codifying
this as an explicit project principle so future fix prompts inherit
the gate by default.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -317,6 +317,32 @@ allowed only with a `TODO TECH-*` reference to a backlog item.
 13. Vue page component in `src/pages/[module]/`
 14. Add route in Vue Router
 
+## Diagnostic discipline: audit before assume
+
+When debugging or fixing any bug, the first action is to verify the
+canonical model against the artifact in question — not to write a fix
+based on the symptom or hypothesis.
+
+This applies to:
+
+- Schema drift (verify the resource shape against the Zod schema, line
+  by line)
+- Filter logic (verify the data model in SCHEMA.md before assuming a
+  controller is wrong)
+- UX divergence (verify the prototype line-by-line, not via spot check)
+- Test failures (verify the assertion matches the documented contract,
+  not the current implementation)
+
+Phase A of every fix prompt is STOP-and-report. No code is written
+before the audit is reviewed.
+
+This principle was formalised after three consecutive incidents where
+initial hypotheses were wrong and the audit gate caught them: B1
+(controller assumed buggy, seeder was wrong), B5 (enum-shape assumed
+drifted, decimals were wrong), and timetable UX (test-passing layer
+diverged from prototype, mechanical-vs-UX split surfaced via browser
+test).
+
 ## User Documentation (VitePress)
 
 End-user documentation lives in /docs/ as a VitePress site.